Modulation system



MODULATION SYSTEM Filed Nov. 25, 1940 3 Sheets-Sheet l VIDEO FREQ.

AMPL.

33 32 40 H/6H-L/6HT 42 NORMAL 7v LINE WIDTH /U0,a6l ysuow HALF-TONE 44 50,.ua YELLOW 4 SHADOW 45 1012a EYELLOW Fig.

r A ASPECT SIZE AND RAT/0 ASPECT RAT/0 VAR/ED IVAR/ED 45 v INVENTOR. -49 ALFRED N. GOLDSMITH ATTORNEY.

Dec. 8, 1942. A. N. GOLDSMITH 2,304,163

MODULATION SYSTEM Filed NOV. 23, 1940 3 S heets-Sheet 2 [N VEN TOR. Al FRED N. 60L 05M! TH BY MQZW A TTORN E Y.

& W4 A. N. GOLDSMITH 2,304,163

MODULATION SYSTEM Filed Nov. 23, 194C- 3 Sheets-Sheet 3 INVENTOR. ALFRED N. GOLDSMITH )KZWW ATTORNEY.

arcades arop'rroa srs'r ed N. @o

we th, New ho, N. Y ignor to be dio mrporation oi erica, New York, N. Y a coratior oi a r application November 23, 19M, Sell No. 368,8?2

a (or. lit-7.5)

application is a continuation in. part oi my application serial screams, filed November l, 1939.

My invention'relates broadly todevices for re-' Presently known television receivers and re producers form the reproduced optical image by means of the action of a moving modulated electron beam which impinges on a fluorescing inaterial, thus producing light due to the fluorescent properties of the material. It has been rec-g;

hired, however, that there are definite limitations attendant the use of such material. The llaht formed is not w ciently intense to b proiected through a lens system onto a larger area with the formation oi an adequately bright image due to the comparative feebleness oi the light in the original image, both becauseoi the fact that large amounts of light are lost in its transmission through lens systems and the fact that the ount of light (light flux in lumcns) per unit area on the screen upon which the magnifled image is cast varies inversely as the square oi the ratio of respective linear dimensions between the magnified image andthe image reproduced on the end of the tube.

The problem of providing a screen which will reproduce an optical image with a light sumciently brilliant to be satisfactorily projected to large, dimensions has been the subject of experimentation by a number of investigators. Screens have been provided of the so-called thermal type, that is, where the light produced .is the direct refiilt of the heating of the screen rather than that due to any inherent fiuorescing properties, and so-called thermal" screens or "thermal images have been utilized for this purpose with varying degrees of success. Accordingly, it is one of the objects of my invention to provide suitable structures for the thermal formation of optical images due to-the energy of impact of a scanning electron beam.

it have found that the shape of the scanning spot which is used plays an important part in the accurate reproduction of a thermal image. This smt should under some definite conditions vary from the circular, as iscommon practice today,

' to the elliptical in shape. Accordingly, it is anof the scanning spot'and, in accordance with the modulation requirements, for the best delineation in the thermal image.

I have found that not only should the shape of the scanning spot be varied under definite circumstances, but that the size of the scanning spot also may be varied in accordance with the variation in the modulation oi! the beam, and it is a further object of my invention to vary the size of the electron scanning spot in accordance with variation in intensity of the electron beam for the purpose of securing optimum delineation inthe'thermal image. Y

One of the drawbacks inherent to themeviously known and described thermal optical image reproducing systems has been that'a comparatively largetemperature change must occur between the normal operating temperatur oi the screen and the temperature at which a brilliant light-is formed. Suitable means may be provided for increasing the thermal sensitivity of such a screen by the use oisu'pplemental heating currents which raise the temperature of the screen to a point where the screen is only feebly visible or just below the temperature at which visible radiation occurs (that is, at low color temperature). Accordingly, it is another of the oban exceedingly high temperature.

vary in accordance with modulation potentials in conjunction with a thermal screen which is biased toa predetermined temperature.

One of the greatest drawbacks to th thermal type of optical image reproducer has been the fact that in order to get a sumciently bright light for projection purposes the thermal screen must be raised at each bright point of the picture to e The result is that sections of the picture which are not as bright as the brightest portions will appear on the thermal screen as a yellowish color rather than a pure white," and accordingly difierent optical intensitiesmay be reproduced in shades of color ranging from .a reddish color on up through an orangeand to a white, dependent upon the optical intensity of the point under reproduction.

This, of course, causes an unpleasant gradation ofdiffering color shades in what should be a. black spot with reference to the direction of motion and white picture. Accordingly, it is another of the objects of my invention to provide means and apparatus for thermally reproducing an optical image in which the unpleasant gradations of 2:231 will be substantially minimized or elimma v the image reproduced in providing a constant color temperature reproduced image by thermal means, the area of the reproducing spot or the shape of the spot a change in the focusing of the electron beam may is utilized in order to produce the constant, color temperature. of course. a combination of some or all of these means may be desirable in order to obtain correct delineation of the reproduced picture. As a result, one or more of th electrode elements or the cathode ray reproducing tube may, of necessity, be energized variably in accordance with the received signals which represent the optical image. all of the electrodes may not be desirable and it may be found preferable todelay the efiect of a signal on some of the electrodes for a short interval of time. Accordingly, it is another of the objects of my invention to provide means and apparatus for associating the energizing of all of the electrodes necessary to produce substantially constant color temmrature on the reproducing screen of a thermal image reproducing tube in such a fashion thatthe best delineation and optimum temperature conditions will be produced and maintained. 7

Accordingly, among the objects of my invention are: 1. To provide suitable structures for the ther-. mal formation of optical images due to the energy of impact of. a scanning electron beam.

2. To provide means for varying the shape of the scanning spot with reference to the direction of motion of the scanning spot in a thermal optical image reconstruction system.

3. To provide meansto vary the size 'ofthe scanning spot in accordance with the variation nannies Simultaneous energizing of garrange'ment.

. Figs. 11, 11a and Fig. i shown relative variation 6i spot size with change in signal intensity.

Fig. d shows a variation in the aspect ratio of the reproducing spot with change in video signal intensity.

I Fig. 4 is a comparative view between the change in aspect ratio only and the change in both size and aspect ratio of the reproducing-spot.

Fig. 5 shows schematically the varying of the sharpness of focus of the scanning spot with changing video siwal intensity.

Fig. d'shows an embodiment of my invention similar to Fig. 1, and in which there is included suitable Mme delay means. v

Figs. '1, 8, and 9' are modifications of my invention Fig. 10 is an aperture lens" electron-optical Fig. 12 is a modification oi the showing of W.- 6-

Fig. 13 is an alternative form of my invention. Fig. i l illustrates a magnetic control system for varying the scanning spot characteristics.

Referring to Fig. 1, there is shown a system embodying my invention. Thisis an enlarged drawing in the plane of the electron gun of a in the modulation of the beam in a thermal optical image reconstruction system. i

4. To provide a thermal optical image reproducing system utilizing a cathode ray beam -forming a spot whose size or shape may vary in accordance with modulation potentials in conjunction with a thermal screen which is biased to a predetermined temperature.

5. To provide means and apparatus for thermolly reproducing an optical image in which the unpleasantgradations of color will be substantially minimized or eliminated.

hinescope. A heater element It is connected to an A. C'. or a D. C. source of power, which in this case is illustrated as being the direct current source of power Ii. Positioned adjacent the heater element is an emissive surface l2, and the electrons -.emitted therefrom pass through the aperture in a control grid It; the latter being connected to the output of the video frequency amplifier iii. the video frequency amplifier being connected in the television receiver. The beam then passes through the aperture in the first anode iii, the latter being energized by a source of power which, in this 'case, is illustrated as direct current source It. 'I'heelement it in turn is connected to a video frequency amplifier l1,

'6. To provide means and apparatus for associating the energizing of all oi the electrodes necessary to produce a substantially constant color'ternperature on the reproducing screen of a thermal image reproducing tube in such afashion that the best delineation and optimum temperature conditions will be produced and My invention in general utilizes a cathodeii'ay 'ducing an optical image. The video signal which is received and whose intensity,. or amplitude. represents the optical intensity or brightness of i not only modulates the cathode ray beam of enthuse, but the same signal is utilized and the characteristics or the spot I formed on the thermal screen are varied in accordance with the modulation intensity .of the. signal. By characteristics I mean that either the spot size or its shape or its focus on the thermal screen is varied, 101' a combination of tube having a thermal type of screen for repro- 1 these spot parameters may be availed of in order to produce a comparatively constant color temperature reproduced image on theYthez-m'al screen.

My invention will be understood best by refer-j ence to the figures in which:

Fig. 1 shows anembodiment of my invention.

'. picture,

.thereto as may be des which are not illustrated here.

whose input is Joined to the output of,video frequency amplifier-Hi so that the potential of the first anode swings around a median value determined by thepotential value of the direct current source It, the swing being either in phase with the potential changes of t e grid It or in opposite phase thereto. or

The potential source it may have a condenser (not shown) shunted across its terminals to permit the ready passage of video frequency charging currents. The scan- I ning beam in the direction as indicated by the armwidentifled as llipasses through the aperture in the focusing second anode iii which is also a positive potential, the potential being supplied by the some of direct current power 20. A condenser 2l-is shunted across the terminals of the source ofdirect-current 2t, and the negative side of the source is connected to the output of a video frequency amplifier 22 having its input "connected to the output of video frequency It. this way the secondanode It may also be I swung in potential at video frequency either in the same or opposite or other phase relationship to the swings of the grid It. The beam then passes through appropriate deflecting fields but which are well mown in the prior' art, and impinges onto the thermal screen it.

The object of the arrangement shown in this figure is as follows: In the bright parts of the the control grid of the electron gun permits maximum beam current to flow thrc' ah the gun. At the same time. the flrst anode mrmits 116 are modifications of Fig. 6.

other phase relation a aumsize of beam, and the second anode iocuses it only to such an extent as to produce a scanning spot of correct size on the grid-like plate or sheet-like plate on which the thermal images are formed. If, however, a halt tone or reduced brightness part of the picture is being scanned, the grid it cuts down the beam current, the first anode may reduce th size of the spot somewhat, and the second anode will focus the spot to a smaller size. The result is that a small.-

er area on the thermal image producing elements;

will be rendered incandescent and accordingly,

' while the light emitted therefrom will be reduced as compared to. that corresponding to a high light, its color temperature will be almost the same. The method of delineation then comprises variable dot areas of more nearly constant color temperature rather than approtely constant dot areas of variable color temperature. hy dot is meant the hypothetical dot element iorming the television picture. The most detial variations oi the elements shown in Fig. 1 may be determined theoretically, but is probably accomplished more conveniently by experimental trial.

It will be seen therefore that this arrangement produces a picture or thermal image which has more nearly the same color in the high lights and half tones. This requires that the range oi temperature with which the image is formed shall be reduced since there is a change in the color of a seli-lmninous body as its temperature is raised. e desired result of'a morenearly constant color temperature in all delineating parts or the thermal image is accomplished by changing the size of the scanning spot in accordance with the video frequency potentials which indicate the brightness of each point oi the as the image gets brighter the scanning spot will increase in size provided a positive image is being formed, and the periphery of the larger scanning spot is shown at ii. The relative size of the smaller scanning spot til is shown by the distance it between the two arrows, and the difl'erence in diameter is indicated by the distance it between the two nearer arrows. ,It will Toe-understood that the size oi the larger scanning spot is sumciently small so as to enable the realization oi full wag detail.

leaving to Fig. 3, there is shown a variation in the aspect ratio of the reproducing spot with"- change in video signal intensity. Thescanning spot it represents a spot for reproducing high lights of the picture. The spot is circular in shape, and for purposes of convenience there has been indicatedthat a current of 100 microarncircular to'iorm an ellipse whose major axis is along the line of scanning. In this case the spot may be produced by current value of only 50 microamperes and, as illustrated at M, the width of the spot will be lessened but the color will remain yellow. For intensities of the video signal representative of shadow the electron beam may be of only 10 microamperes intensity and the aspect ratio is changed to a still greater degree than in the case of the half tone, as illustrated at tt,

the reproducing spot. The section of this figure which is labeled "aspect ratio only varied comprises a recapitulation of the subject matter 'ilsirable adjustment of the video frequency potenhigh lights of a picture.

lustrated in Fig. 3, and similar numbers have been applied to the scanning spots. In addition to varying the aspect ratio only, both the size of the scanning spot and the aspect ratio as well may be varied. The spot l'i represents the same spot asthat indicated at it and-as in the case of the spot it, represents relativelywhat might be the size of a scanning spot for-reproducing similarly to the scanning spot it, would represent relatively a scanning spot for reproducing the half tone in a picture where both the aspect ratio and the spot size has been varied. The

scanning spot it, similarly to the scanning spot scanning spot with changing video signal intensity. The scanning spot it represents a spot for indicated by advancing through a dotted line the spot hi to be included in the spot iii,'and the diameter shown is the distance it between the nearer arrows. It will be noticed that the modified scanning spot ti has a vague or relatively soft contour, and apparently is larger than the sharply focused unmodified spot ht.

Referring to Fig. 6, there is shown an embodiment of my invention similar to Fig. 1, and in which there is included suitable time delay means. In this figure a heating element tithes positioned in omrative relationshipv thereto an electron emitting element ti and the electrons emitted therefrom pass through the aperture of a control electrode M. The beam so formed then passes through the aperture of the first anode t3 and thence between the plates forming peres intensity will produce such a spot. The

arrow iii shows the normalscanning direction, that is from left to right. It. will be seen that this may produce a yellow color as illustrated a'it ti, and the normal line width is'so labeled. (3n the other hand, for half tone intensity the aspect ratio of the scanning spot it is indicated, and it will be seen that the spot is compressed from the the second, anode 8t. The second anode St is energized through the D. C. source of potential,

video frequency voltages to reach the element St without passing through the l). C. source of potential. Also connected to the second anode it through the battery is a circuit arrangement t1 into whichis fed the video signal by means of the. leads St. The element 61 may contaih amplifying apparatus and may also contain time The scanning spot it,

delay arrangements. sinceit be appreciated that not only do the video oi have to be will be appreciated that an us modulotion potential impressed onto the control electrode will shoot a particular section-of the beam,

and this particular section will not reach the second anode until a short time later and the same modulation potential which has adected this section of the .beam at the control electrode should then afiect the same section of the beam at the second anode. Further, there may be other relative time difierences between controls applied to the beam by various electrodes, and

such time diflerence's may require compensation.

Hence a time control means, must be insertedv either with reference to the control electrode iii or the second anode til. Referring to Fig. "I, there is shown an alternative form of the arrangement disclosed in Fig. 6. In this figure the first anode is indicated as it and the second anode as H. Thesecond anode is energized with a source of steady direct current potential it and the video are introduced through the pliiym anddelaying arrangement it by way of leads id in parallel to the anode voltage obtained from the source it. A video frequency choke it is inserted in the lead connecting-the anode voltage" to the cathode tube. A condenser might also be iniii) aement wherein the second anode Mil of serted in the lead "it to isolate the circuit on rang'eznent it from the high voltage anode source.

Referring to Fig.6, there is shown a somewhat similar arrangement to the in Fig. 6. .In this case; however, thevideo potenmanner described with respect togfthe elements so ill and it of Figs. 6 and 7, respectively. The second anode is indicated as at. p M

Referring to Fig. 9,'there is shown an arrang ment which is 'alternative to the showing oi Fig. 7. In Fig. 9 the video signalssre impressed by means of leads ct through delay and amplifying circuits 98 onto the first anode. d2 of the tube.

this figure-there is shown the heating element rather than the'second anodeas illustrated in Fig. 7-. Similarly the lead lit might have a conj denser inserted serially therewith toprevent impressing of the anode voltage from the source 9t onto the circuitscontained in it. A video frequency choke it isinsertedin series with the source of anode potential" to suppress the impression of video frequency si onto the cirsteady direct potential WW.

cult-containing the source of anode potential.

The second anode is indicated at it."

There has] been brought out above'that to control the size and/orsharpness of focus as aaoaaea v it is also possible to throw the sea spot out of focus toany desired extent by the video signal, or to its size, or to alter its optical aberrations through the use, for. example, of the so-called electron aperture lens" which may be of the so-called divergent type, the degree of divergence bein'g video signal controlled. Errors in the electron optics of the scanning spot production, as well as changes in the aspect ratio thereof, can be introduced by decentering or asymmetry of the electron optical electrodes or .aperturestherein or the shape thereof.

Referring to Fig. 10, there is shown schematically an example of the so-called aperture lens." This consists of a large fiat surface it!) on which there is placed an electron emitting material iti and in front of and close to which is a parallel plate tilt in which is the focusing aperture iiiil. In this instance, the-video signal control voltages are applied to the element ltd.

Referring to Fig. 11, there is shown a typical the tube is elliptical in cross-section rather than circular, as indicated in the view thereof shown in Fig. 11b, and in which the anode is identified as iii. In this figure the neck of the tube is shown in cross-section with the elliptically shaped second anode. This element is made elliptical deliberately to introduce eccentricity or astigmatism into the scanning spot. and to en-' able, if desired, the video signal control of the degree or extent of such eccentricity by impressing the video signals onto the second anode tit. Thefirst anode lit remains of circular cross section as indicated in Fig. 11a, in which the necl:

of the tube isshown in cross-section and the circular shaped anode is identified as iii. Alternatively, the first anode iii could'be given an elliptical cram-section and the apertures lid and i it within the plates-might be made ellipti cal for the same purpose. seen that either or both of these anodes may have an elliptical cross-section.

Referring to Fig.' 12,. there is shown an arrangement for deliberately introducing eccentricity or astigmatism into the scanning spot by decantering either or both the first anode ltd or the second anode it! relative to the axis of symmetry tilt of thebeam. In this e the heating element lid is energized by either alternating or direct current and causes electron emission from the electron emissive material lit. These electrons are concentrated into a beam and maybe modulated by the control-electrode tit.

Reierrlngto Fig. 13, there is shown a diderent and alternative method'of controlling the scanning spot characteristics by the video signal. In

lid with theelectron emissive material idl and the apertured control electrode its.

anode is shown at ltd and the second anode at ti t, the latter being energized by a source of V In addition to the first and second anodes tat and let respectively, there is a third or supplementary electrode lit to which there may be applied the video signal voles from the leads IN and the amplifying and delaying arrangement Hit. Of course,.

biasing potential may also be applied to the supplementary anode we in such manner as indicated, for instance, in Figs. 6 and 7.

The arrangement as indicated in 13 has the advantage that it enables the independent control by the video signal of the scanning begin characteristics other than the intensity. It will Accordingly. t Will a The first asoaioa be understood that the intensity of the beam may be varied slightly and to a minor extent by the means shown in the figures of this specification for the control of the other characteristics of the scanning spot. However, these methods shown will predominantly and primarily and sub stantially entirely control other characteristics of the scanning spot than its intensity.

Referring to Fig. 14, there is shown an apparatus for the magnetic method for video signal control of the scanning spot characteristics other than its intensity. Inthis arrangement the coil Mid is the usual magnetic focusing coil and, this partures of the particular arrangements hereinbefore illustrated which will fall fairly within the spirit and'scope of my invention and I am not limited tat-he exact showings, but claim all .optical'image are impressed.

beam at the scanning spot are altered in accordance with the value of the signals impressed on said acceleratingmeans to enhance the accuracy of reproduction of the reproduced image.

4. Apparatus in accordance with claim 3, wherein said electron beamaccelerating means comprises a plurality of anode electrodes upon each of which the signals representative of the 5. Apparatus in accordance with claim 3, and wherein there is provided in addition time delay means for controlling the time of impression of the signals indicativeof the optical values of the image to be reproduced onto at least one of the beam modulating electrodes relatively to the other-beam modulating electrodes.

6. Apparatus in accordance with claim 3, comprising, in addition, a time delay circuit between said beam modulating and accelerating ,means so that signals representative of the optical intensities of the optical image to be reproduced may be applied with predetermined time delay to the modulating and the' accelerating means for controlling said cathode ray beam.

7. Apparatus in accordance -with I wherein said anode means for accelerating said such modifications as fall fairly within the spirit and scope of the hereinafter appended claims.

What I claim is:

l. In an electro-optical image reproducing system, means for developing a cathode ray beam, a thermally responsive target positioned to receive the said electron beam to develop light at the area of beam impact, and means operating under the control of applied signal modulation potentials to alter at least one of the cross-sectional dimensional parameters of aspect ratio and shapness of focus of the impact point formed by the electron beam on the target to maintain substantially monochromatic'im'age reproduction from the target.

2. In an electro-optical image reproducing systeym, means for developing a cathode ray beam, a thermally responsive target positioned to receive the said electron beam to develop light-at the area of beam impact, and means for'modulating the said developed electron beam under the control of applied signals, said modulation being adapted to vary the total electron beam current in substantial proportion to the modulation signal and simultaneously to maintain the beam current density across the cross-sectional areas of the said beam substantially constant so that the light image developed upon the said target is substantially'monochromatic.

3. In .an electro-optical image reproducing system, means for developing a cathode ray beam, means for modulating the. intensity of the beam under the control of signals indicative of the optical values of the optical image to be reproduced, a target means for producing light in accordance with the impingement of the electron beam thereon, means for accelerating the cathode ray beam in the direction of the target and means for nnpressing signals representative of the optical image onto said electron beam accelerating means whereby at least one of the cross-sectional dimensional parameters or said electron beam hasfat least a portion thereof hav- :ing an elliptically shaped cross-section.

8, Inan optical image reproducing system in which signals are receivedindicative of the intensities of the optical values of the image to be reproduced, and in which the image is re-' produced by the-thermal effect of acathode ray beam impacting an incandescing electrode, the method of maintaining .a constant color temperature. inthe screen over a range of signal variations which comprises the steps of generating a cathode ray beam and directing the generated beam toward the 'incandescing electrode, modulating the current value of said beam in accord.- ance with the value of the instantaneous signal potentials so as to alter at leastpne of the crosssectional dimensional parameters of aspect ratio and focus of said beam-in accordance with the same instantaneous signal, values so as to maintain substantial monochromatic image reproduction from the incandescing electrode.

9. In an optical image reproducing system in which signals are received indicative of. the intensities of the optical values of the image to be reproduced,- and in which the image is reproduced by the action of the electron beam on a thermally responsive target electrode, themeth- 0d of reproducing the optical imagewhichincludes the steps of generating a cathode ray beam and directing the beam toward the target electrode and modulating thecurrent value of said electron beam in accordance with the instantaneous values of the signals representative of the optical image to be produced upon the target by varying the total electron beam current in substantial proportion to the said signals and simultaneously maintaining the beam current trode is substantially monochromatic in character. v v

' AII'RED N GOLDSMITH.

claim 3, 

